In the art of locks, wafer tumbler locks are well known. A wafer tumbler lock is a type of lock that uses a set of flat tumblers or “wafers” to prevent the lock from opening unless the correct key is used in combination with the lock. In such locks, the tumblers are typically rectangularly-shaped single piece structures that fit into, and are movable within, slots that are defined within a lock cylinder. Each tumbler is spring-loaded which biases the tumbler in one direction or another which, in turn, causes it to protrude from the cylinder and into longitudinally-formed, or axially-formed, grooves defined within an outer casing of the lock. As long as one end of one of the tumblers protrudes into one of the grooves, rotation of the cylinder is prevented and the lock remains locked. A rectangular hole or “window” is formed in the center of each tumbler to allow passage of a key through the hole. The vertical position of the hole is intentionally varied between tumblers so that a key must have notches that correspond to the height of the hole in each tumbler such that each tumbler is pulled inwardly to the point where the tumbler edges are flush with the outer surface of the lock cylinder and clear the way for the cylinder to rotate within the casing. If any tumbler is insufficiently raised, or raised too much, a tumbler edge will be situated within the groove of the casing thereby preventing rotation of the cylinder within the casing. Such would be the case where no key is inserted into the lock or where the use of an improperly profiled key is inserted.
These inventors are aware of the need to provide such a wafer tumbler lock with a master key capability for the purpose of allowing locks to use multiple keys and master keys without requiring the lock to be fabricated through the coordination of a large number of different part numbers used in the lock. These inventors are also aware of the need to provide such a lock that is “backwards compatible” with existing locks. Accordingly, it is an object of the present invention to provide a new and useful master keying lock, system and method that would provide a lock that can be unlocked with an original key provided for the lock as well as with one or more master keys. It is another object of the present invention to provide such a lock that utilizes existing tumblers and lock keys to accomplish that functionality. It is still another object of the present invention to provide such a lock which is also more secure and less prone to being “picked” because the sleeve within the system cannot be pushed back into the lock case without use of a master key.